An insecticide is a compound that controls insect life. Insect life may be controlled by killing a substantial proportion of an insect population. Compounds which control insect life in this manner must be highly toxic to the insect population and non-toxic to other living things.
Insecticides may be applied to an area where it is desired to control insect life by a variety of methods. These methods include topical application and systemic application.
Topical application is application of the insecticide directly to the area where the insect desired to be controlled is present or may light. Insecticides applied topically remain localized near the site of application.
By contrast, systemic insecticides are applied to a site remote from the area where the insect to be controlled is present or may light. A systemic insecticide is capable of freely translocating within a living body. The insecticide translocates within the living body from the site of application to the area where the insect to be controlled is present. The insect is killed in the area where it is present. The living body through which the insecticide has translocated remains unharmed.
Whatever the method of application, a certain minimum amount of a compound is effective to control insect life. This amount is the "insecticidally effective amount."
Insecticides are commonly used to control insects which are harmful to man. Insects may be harmful to man either directly, e.g. by carrying disease, or indirectly, e.g., by destroying animal life, plant life, food products, or other commodities.
Blowflies are an example of an insect which destroys animal life. Screwworm flies are a type of blowfly which present a particular problem.
Screwworms populate warm climates. They are found in the southern United States, including Texas, New Mexico and Arizona, and Central and South America. These insects are dangerous to cattle, hogs, horses, mules, sheep, goats, dogs and other domestic and wild animals.
Screwworms attack a host animal, e.g., cow, hog, etc., at an open wound or other diseased body opening and lay their eggs at the site of the opening. Screwworm larvae feed on the wound or opening and invade healthy tissue surronding it. Infestation of an opening in this manner prevents the opening from healing.
The odor of an infested opening attracts additional flies, including other types of blowflies, to the opening. The newly attracted flies lay their eggs near the infested opening. Successive generations of insects cause a serious inflammation. Unless the blowfly infested opening is treated effectively, death of the host animal is inevitable.
To date, treatment of openings attacked by screwworms has been limited to application of a topical smear. Care must be taken to insure that the entire infested area has been completely covered by the smear. It is difficult to protect inaccessible areas of the animal in this manner.